README: remove outdated repositories block added during merge

Author: greenrobot-team

README.md

@@ -191,13 +191,6 @@ plugins {
     // Add the ObjectBox plugin
     alias(libs.plugins.objectbox) apply false  
 }
-
-allprojects {
-    repositories {
-        // Add Maven Central to the dependency repositories
-        mavenCentral()
-    }
-}
 ```
 
 ```kotlin
@@ -260,13 +253,6 @@ plugins {
     // Add the ObjectBox plugin
     id("io.objectbox") version "5.3.0" apply false
 }
-
-allprojects {
-    repositories {
-        // Add Maven Central to the dependency repositories
-        mavenCentral()
-    }
-}
 ```
 
 ```kotlin